Airbag modules are known with a module housing that has an airbag deployment opening with a predetermined opening dimension, and with an airbag that is arranged folded in the module housing, said airbag having a first wall and a second wall situated opposite from the first wall.
The module housing can have many different forms. In the case of knee-protection airbag modules or passenger-side airbag modules that are installed in the region of the dashboard, the module housing is usually trough-shaped and has an elongated, largely rectangular airbag deployment opening. When the airbag module is activated, gas flows out of a gas generator into the airbag while the airbag is still inside the module housing. Consequently, the side walls of the module housing are subjected to stress during the first deployment phase of the airbag. In order to prevent this from causing an expansion of the module housing, also called bulging, the module housing is often reinforced, for example, by ribs or by thicker walls.
In U.S. Pat. No. 4,842,300, in order to prevent such bulging, the opposite side walls of the module housing are joined by a tether strap located in the middle of the airbag deployment opening. This tether strap inevitably extends through the airbag as well. When the force of the inflating airbag is exerted on the housing, this force is countered by the tension of the tether strap on the housing side walls, the strap limiting the distance between the side walls.